Processing stacked substrates

ABSTRACT

Representative implementations provide techniques for processing integrated circuit (IC) dies and related devices, in preparation for stacking and bonding the devices. The disclosed techniques provide removal of processing residue from the device surfaces while protecting the underlying layers. One or more sacrificial layers may be applied to a surface of the device during processing to protect the underlying layers. Processing residue is attached to the sacrificial layers instead of the device, and can be removed with the sacrificial layers.

PRIORITY CLAIM AND CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of and claims the benefit of U.S.Non-Provisional application Ser. No. 16/921,110, filed Jul. 6, 2020,which is a continuation of U.S. Non-Provisional application Ser. No.15/846,731, filed Dec. 19, 2017, which claims the benefit under 35U.S.C. § 119(e)(1) of U.S. Provisional Application No. 62/439,771, filedDec. 28, 2016, both of which are hereby incorporated by reference intheir entirety.

FIELD

The following description relates to processing of integrated circuits(“ICs”). More particularly, the following description relates to removalof processing residue from the surface of dies, wafers, and othersubstrates.

BACKGROUND

The demand for more compact physical arrangements of microelectronicelements such as integrated chips and dies has become even more intensewith the rapid progress of portable electronic devices, the expansion ofthe Internet of Things, nano-scale integration, subwavelength opticalintegration, and more. Merely by way of example, devices commonlyreferred to as “smart phones” integrate the functions of a cellulartelephone with powerful data processors, memory and ancillary devicessuch as global positioning system receivers, electronic cameras, andlocal area network connections along with high-resolution displays andassociated image processing chips. Such devices can provide capabilitiessuch as full internet connectivity, entertainment includingfull-resolution video, navigation, electronic banking and more, all in apocket-size device. Complex portable devices require packing numerouschips and dies into a small space.

Microelectronic elements often comprise a thin slab of a semiconductormaterial, such as silicon or gallium arsenide. Chips and dies arecommonly provided as individual, prepackaged units. In some unitdesigns, the die is mounted to a substrate or a chip carrier, which isin turn mounted on a circuit panel, such as a printed circuit board(PCB). Dies can be provided in packages that facilitate handling of thedie during manufacture and during mounting of the die on the externalsubstrate. For example, many dies are provided in packages suitable forsurface mounting. Numerous packages of this general type have beenproposed for various applications. Most commonly, such packages includea dielectric element, commonly referred to as a “chip carrier” withterminals formed as plated or etched metallic structures on thedielectric. The terminals typically are connected to the contacts (e.g.,bond pads) of the die by conductive features such as thin tracesextending along the die carrier and by fine leads or wires extendingbetween the contacts of the die and the terminals or traces. In asurface mounting operation, the package may be placed onto a circuitboard so that each terminal on the package is aligned with acorresponding contact pad on the circuit board. Solder or other bondingmaterial is generally provided between the terminals and the contactpads. The package can be permanently bonded in place by heating theassembly so as to melt or “reflow” the solder or otherwise activate thebonding material.

Certain packages, commonly referred to as “chip scale packages,” occupyan area of the circuit board equal to, or only slightly larger than, thearea of the device incorporated in the package. This scale isadvantageous in that it reduces the overall size of the assembly andpermits the use of short interconnections between various devices on thesubstrate, which in turn limits signal propagation time between devicesand thus facilitates operation of the assembly at high speeds.

Semiconductor dies can also be provided in “stacked” arrangements,wherein one die is provided on a carrier, for example, and another dieis mounted on top of the first die. These arrangements can allow anumber of different dies to be mounted within a single footprint on acircuit board and can further facilitate high-speed operation byproviding a short interconnection between the dies. Often, thisinterconnect distance can be only slightly larger than the thickness ofthe die itself. For interconnection to be achieved within a stack of diepackages, interconnection structures for mechanical and electricalconnection may be provided on both sides (e.g., faces) of each diepackage (except for the topmost package). This has been done, forexample, by providing contact pads or lands on both sides of thesubstrate to which the die is mounted, the pads being connected throughthe substrate by conductive vias or the like. Examples of stacked chiparrangements and interconnect structures are provided in U.S. PatentApp. Pub. No. 2010/0232129, the disclosure of which is incorporated byreference herein.

However, some stacked arrangements where the surfaces of dies or devicesare in intimate contact or proximity to each other are sensitive to thepresence of particles or contamination (e.g., greater than 0.5 nm) onone or both surfaces of the stacked dies. For instance, particlesremaining from processing steps can result in poorly bonded regionsbetween the stacked dies. Temporary bonding of dies and substrates, forprocessing or handling, can be particularly problematic, since removalof temporary carriers and substrates can leave behind bonding layerresidue.

Residue from temporary bond layers, which can be comprised of hightemperature polymers, can be discontinuous with varying thicknesses onthe substrate surface (e.g., thickness may range from 50 nm to 30 um).Plasma ashing can be used to remove thin residue, but even long oxygenplasma ashing steps (e.g., over 40 minutes) may not remove the thickestresidues, and in many instances, may oxidize the conductive interconnectlayer, for example, a copper interconnect layer. In such cases, a hightemperature (e.g., over 50° C.) wet process is sometimes used to removethick residue; however, the process may not be compatible with other dielayers or materials. For instance, the high temperature wet process candegrade the smoothness of the polished metal layers, reducing deviceyield.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is set forth with reference to the accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number first appears. Theuse of the same reference numbers in different figures indicates similaror identical items.

For this discussion, the devices and systems illustrated in the figuresare shown as having a multiplicity of components. Variousimplementations of devices and/or systems, as described herein, mayinclude fewer components and remain within the scope of the disclosure.Alternately, other implementations of devices and/or systems may includeadditional components, or various combinations of the describedcomponents, and remain within the scope of the disclosure.

FIG. 1 is a schematically illustrated flow diagram illustrating anexample die processing sequence.

FIGS. 2 and 3 show a schematically illustrated flow diagram illustratingan example die processing sequence, according to a first embodiment.

FIGS. 4 and 5 show a schematically illustrated flow diagram illustratingan example die processing sequence, according to a second embodiment.

SUMMARY

Representative implementations provide techniques for processingintegrated circuit (IC) dies and related devices, in preparation forstacking and bonding the devices. Processed devices can be left withsurface residue, negatively affecting bonding. The disclosed techniquesimprove residue removal from the device surfaces while protecting theunderlying layers. One or more sacrificial layers may be applied to asurface of the device during processing to protect the underlyinglayers. Processing residue attached to the sacrificial layer(s) insteadof the device can be removed with the sacrificial layer(s).

In various implementations, example processes include wet etching thesurface of the device to remove the sacrificial layers and residue. Insome embodiments, one or more of multiple sacrificial layers are removedat different processing stages to protect underlying layers during theprocessing stages. In some examples, a selective etchant (a wet etchant)may be used to remove one or more sacrificial layers and residue withoutdamaging the surface of the device or damaging metallic interconnectstructures on the surface of the device.

Various implementations and arrangements are discussed with reference toelectrical and electronics components and varied carriers. Whilespecific components (i.e., wafers, integrated circuit (IC) chip dies,etc.) are mentioned, this is not intended to be limiting, and is forease of discussion and illustrative convenience. The techniques anddevices discussed with reference to a wafer, die, or the like, areapplicable to any type or number of electrical components, circuits(e.g., integrated circuits (IC), mixed circuits, ASICS, memory devices,processors, etc.), groups of components, packaged components, structures(e.g., wafers, panels, boards, PCBs, etc.), and the like, that may becoupled to interface with each other, with external circuits, systems,carriers, and the like. Each of these different components, circuits,groups, packages, structures, and the like, can be generically referredto as a “microelectronic element.” For simplicity, such components willalso be referred to herein as a “die” or a “substrate.”

The disclosed processes are illustrated using graphical flow diagrams.The order in which the disclosed processes are described is not intendedto be construed as a limitation, and any number of the described processblocks can be combined in any order to implement the processes, oralternate processes. Additionally, individual blocks may be deleted fromthe processes without departing from the spirit and scope of the subjectmatter described herein. Furthermore, the disclosed processes can beimplemented in any suitable manufacturing or processing apparatus orsystem, along with any hardware, software, firmware, or a combinationthereof, without departing from the scope of the subject matterdescribed herein.

Implementations are explained in more detail below using a plurality ofexamples. Although various implementations and examples are discussedhere and below, further implementations and examples may be possible bycombining the features and elements of individual implementations andexamples.

DETAILED DESCRIPTION Overview

Various embodiments of techniques for processing integrated circuit (IC)dies and related devices, in preparation for stacking and bonding thedevices, are disclosed. Devices undergoing processing can be left withsurface residue from the process steps, negatively affecting bonding.The disclosed techniques improve residue removal from the devicesurfaces while protecting the underlying layers.

In various embodiments, using the techniques disclosed can simplify thestacking process for minimal tolerance stacking and bonding techniques,reduce die fabricating and processing costs and improve profit margins,reduce defects in temporary bonding operations, allow for higher stackeddevice yield, eliminate key process defects, and can reduce handling ofdies to minimize particle generation. Dies to be stacked and bondedusing surface to surface direct bonding techniques without adhesive,such as “ZIBOND®,” and/or hybrid bonding, such as “Direct BondInterconnect (DBI®)” both available from Ziptronix, Inc., a XperiTechnologies company (see for example, U.S. Pat. Nos. 6,864,585 and7,485,968, which are incorporated herein in their entirety), which canbe susceptible to particles and contaminants due to the need for anextremely flat interface, can particularly benefit. The removal ofparticles between opposing insulator, semiconductor, and/or conductorlayers improves the flatness of the surfaces and, accordingly, theability of the two surfaces to bond.

For example, a graphically illustrated flow diagram is shown at FIG. 1 ,illustrating an example die processing sequence 100. At block (A) theprocess begins with preparing a substrate assembly by bonding asubstrate handle 104 to a substrate 102 including one or more devices(devices not shown) using a temporary bonding layer 106. Wiring layers108 of the substrate 102 are comprised of a metal (such as copper,etc.), and are contacted by the bonding layer 106. In various examples,the bonding layer 106 is comprised of a high temperature polymer, anepoxy, polyimide, an acrylic, or the like, to ensure the handle 104remains bonded to the device 102 during processing.

At block (B), a portion of the back side of the substrate 102 is removedto the desired dimensions, using one or more techniques (e.g., grinding,chemical mechanical polishing/planarizing (CMP), reactive-ion etching(RIE), etc.). The backside of the thinned substrate 102 may be processedfurther, for example, to form an interconnect routing layer, a passivecomponent layer, or other structures or features of interest. At block(C), the substrate 102 with one or more devices is attached to a dicingsheet 110 for singulation. The handle substrate 104 is now on the“topside,” in preparation for its removal.

At block (D), the handle 104 may be removed, by grinding, etching,polishing, sliding off, or by optical degrading of the temporary bondingadhesive layer 106, etc.). At block (E), the temporary bond layer 106 isremoved. As shown at block (E), the removal process typically leavessome residue 112 behind. The residue 112 can have varying thicknesses(e.g., thickness may range from 5 nm to 30 um, or even higher). Plasmaashing can be used to remove thin residue 112, but even long oxygenplasma ashing steps (e.g., over 40 minutes) may not remove the thickestresidues 112, and in many instances, may oxidize the wiring layer 108,for example, a copper interconnect layer 108. Longer ashing times alsomay roughen the surface of the exposed wiring layer 108, which canreduce the yield of the bonded devices. In some cases, a hightemperature (e.g., over 50° C.) wet etch process is used to remove thickresidue 112; however, the process may not be compatible with other dielayers or materials. For instance, the high temperature wet process candissolve portions of the surface the conductive metals of the wiringlayer(s) 108, thus degrading the metal wiring layer(s) 108, removingmore metal than is desirable and leaving a rough surface topography. Insome low-tolerance bonding methods, such as “ZIBOND®” and “Direct BondInterconnect (DBI®)”, it is desirable for the metal topography (e.g., ofthe wiring layer(s) 108) to have less than 10 nm variance for successfulbonds.

At block (F), the substrate 102 is singulated into dies 114. As shown,the residue 112 may remain on the dies 114, potentially resulting inpoor bonding, and reduced product yield.

Example Implementations

In various implementations, one or more protective layers can be appliedto sensitive device layers prior to bonding carriers or handlesubstrates to the sensitive layers. Removal of the protective(sacrificial) layer(s) also removes any residue left when removing thebonding layer. In various embodiments, the protective layer may beremoved using a room-temperature or near room-temperature process thatdoes not damage the underlying sensitive insulating and conductivelayers.

For example, FIGS. 2 and 3 show a graphically illustrated flow diagramillustrating an example die processing sequence 200, according to afirst embodiment. As shown in FIG. 2 at block (A), prior to applying thetemporary adhesive 106 and handle substrate 104, a thin inorganicprotective layer 202 is formed (spun on, for example) over the wiringlayer 108 of the substrate 102. In various embodiments, the protectivelayer 202 may comprise one or more of SiO2 (silicon dioxide), B—SiO2(i.e. boron doped silicon dioxide), P—SiO2 (i.e. phosphorus dopedsilicon dioxide), or the like. In other embodiments, the protectivelayer 202 may comprise a non-stoichiometric dielectric material(non-device quality dielectric material) coated by a lower temperatureplasma enhanced chemical vapor deposition (PECVD), an atomic layerdeposition (ALD), a plasma enhanced atomic layer deposition (PEALD), orlike methods. The protective layer 202 may be less than 50 nm thick insome embodiments (thicker or thinner in other embodiments). As part ofthe process, depending on the nature of the coating process, theprotective layer 202 may be cured at a temperature less than 100° C. ininert gas or vacuum for approximately 30 minutes. In various otherimplementations, the curing temperature and time and ambient environmentmay vary. In some cases, the protective layer 202 may be subsequentlytreated with plasma radiation prior to adding the adhesive layer 106.

At block (B) the substrate 102 including one or more devices (devicesnot shown) is bonded to a handle substrate 104 using a temporaryadhesive 106, as described above. In the example process 200, the bondlayer 106 contacts the protective (sacrificial) layer 202 instead ofcontacting the metal wiring layer 108. In this way, the sensitivemetallic wiring layer 108 is protected from the adhesive 106 and itsresidue 112. At block (C), the substrate 102 is reduced as desired forthe intended application and processed further as needed. At block (D),the reduced substrate 102 is attached to a dicing sheet 110, with thehandle 104 topside.

At block (E), the handle 104 is removed, and at block (F), the temporarybond layer 106 is removed, leaving residue 112 behind. In this exampleprocess 200, the residue 112 is left on the protective layer 202 ratherthan the metal wiring layer 108. In some other embodiments, theundesirable residue 112 may be residue from the dicing sheet or grindingsheet adhesive. Regardless of the source of the undesirable residue 112,the devices utilizing the substrate 102 are formed in such a sequencethat the undesirable residue 112 is in contact with the protectivesacrificial layer 202.

Referring to FIG. 3 , the process 200 is continued. Block (F) isillustrated again in FIG. 3 for continuity and ease of discussion. As anoptional process step, at block (F) the residue 112 may be exposed tooxygen plasma, for less than 10 minutes for example, to remove thethinner residue 112. In an embodiment, the plasma exposure can alsoincrease the hydrophilicity and weaken the bonds in the coated inorganicprotective layer 202, and make the protective layer 202 and the residue112 easier to clean off the substrate 102. At block (G), the substrate102 is singulated into dies 114. As shown at block (G), residue 112 mayremain (or further accumulate) on the dies 114, on the protective layer202, after singulation.

At block (H), a wet dilute etchant 302 (e.g., buffered oxide etchant(BHF), hydrofluoric acid (HF), glycated dilute BFH or HF, or the like),for instance, with fluoride ions concentration less than 2% andpreferably less than 0.2%, is sprayed onto the dies 114 to break up andremove the inorganic protective layer 202. In some embodiments, it ispreferable that the etchant 302 includes a complexing agent to suppressthe etching of the metal in the wiring layer 108 beneath the protectivelayer 202. The complexing agent may comprise, for example where theconductive metal is copper, a complexing agent with a triazole moiety,or the like. The wet etchant 302 may be applied by spin process (asillustrated), another batch process, or the like, for a preselectedduration of time, as desired. The complexing agent may be removed in asubsequent cleaning operation with a suitable solvent, for example, asolvent containing an alcohol.

At block (I), the singulated dies 114 are shown free from residue 112.The removal of the protective layer 202 also removes the residue 112from the surface of the dies 114, without degrading the wiring layer 108of the dies 114. In an embodiment, as shown at blocks (J) and (K), oneor more additional inorganic (or organic, in alternative embodiments)protective layers 304 are shown as having been previously added to thesecond (opposite) surface of the substrate 102. For instance, in variousimplementations, the additional protective layer(s) 304 can beoptionally added to the second surface of the substrate 102 to protectthe substrate 102 during various processes. The protective layer(s) 304may be added prior to locating the substrate 102 onto the dicing sheet,for instance (see block (D)). In such an embodiment, the protectivelayer(s) 304 may protect the second surface of the substrate 102 fromresidue or adhesive associated with the dicing sheet, or may facilitatecleaning such residue from the second surface of the substrate 102. Atblock (J) the substrate 102 is shown singulated into dies 114 and atblock (K) the substrate 102 is shown intact.

Another example die processing sequence 400 is shown at FIGS. 4 and 5 ,according to various embodiments. In the embodiments, two or moreprotective layers 202 and 402 are applied to the metal wiring layer 108prior to the adhesive 106. In an embodiment, the wiring layer 108 isprotected with an organic protective layer 402 (such as an organicresist, or the like), and the organic protective layer 402 is protectedby the inorganic protective (sacrificial) layer 202, as discussed above,prior to bonding the handle substrate 104 to the substrate 102. In theembodiments, the use of additional protective layers (such as theprotective layer 402) allows underlying layers (such as the wiring layer108) to be protected while exposed layers are processed. For instance,the additional organic protective layer 402 allows the protective layer202 to be removed using chemicals and/or techniques that may be harmful(e.g., corrosive, roughening, depletive) to the wiring layer 108.

Referring to FIG. 4 , at block (A), the substrate 102 including one ormore devices (devices not shown) is initially coated with a thin (spunon, for example) organic protective layer 402 over the wiring layer 108,followed by the thinner inorganic protective layer 202 (e.g., SiO2,B—SiO2, P—SiO2, and the like), as described above.

At block (B) the substrate 102 is bonded to a handle substrate 104 usinga temporary bond 106, as described above. Also in this example, the bondlayer 106 contacts the protective (sacrificial) layer 202 instead ofcontacting the metal wiring layer 108 or the organic layer 402. At block(C), the substrate 102 is reduced as desired, and at block (D), thereduced substrate 102 is attached to a dicing sheet 110, with the handle104 topside.

At block (E), the handle 104 is removed, and at block (F), the temporarybond layer 106 is removed, generally leaving residue 112 behind. Also inthis example, the residue 112 is left on the protective layer 202 ratherthan the metal wiring layer 108 or the organic layer 402.

Referring to FIG. 5 , the process 400 is continued. Block (F) isreproduced at FIG. 5 for continuity and ease of discussion. Optionally,at block (F) the residue 112 may be exposed to oxygen plasma, for lessthan 10 minutes for example, to remove the thinner residue 112 layer andalso to increase the hydrophilicity and weaken the bonds in the coatedinorganic protective layer 202. This can make the protective layer 202and the residue 112 easier to clean off the substrate 102. At block (G),the substrate 102 is optionally singulated into dies 114. As shown, theresidue 112 may remain on the dies 114, on the protective layer 202. Atblock (H), a wet dilute etchant 302 (e.g., buffered oxide etchant (BHF),hydrofluoric acid (HF), or the like), is sprayed onto the dies 114 tobreak up and remove the inorganic protective layer 202. The wet etchant302 may be applied by spin process, or the like, for a preselectedduration of time as desired. The protective organic layer 402 remains onthe dies 114.

At block (I), the singulated dies 114 are shown substantially free fromresidue 112. The removal of the protective layer 202 also removes theresidue 112 from the surface of the dies 114, without degrading thewiring layer 108, at least in part due to the protective organic layer402 over the wiring layer 108. In an embodiment, as shown at blocks (J)and (K), one or more additional inorganic or organic protective layer304 are shown as having been previously added to the second (opposite)surface of the substrate 102. For instance, in various implementations,the additional protective layer(s) 304 can be optionally added to thesecond surface of the substrate 102 to protect the substrate 102 duringvarious processes. The protective layer(s) 304 may be added prior tolocating the substrate 102 onto the dicing sheet, for instance (seeblock (D)). In such an embodiment, the protective layer(s) 304 mayprotect the second surface of the substrate 102 from residue or adhesiveassociated with the dicing sheet, or may facilitate cleaning suchresidue from the second surface of the substrate 102. At block (J) thesubstrate 102 is shown singulated into dies 114 and at block (K) thesubstrate 102 is shown intact.

In one embodiment, after the removal of the temporary bonding layer 106as depicted in FIG. 1 at block (E), FIG. 3 at block (F) and FIG. 5 atblock (F) for example, the undesirable residue 112 may be removed byremoving the layer 202 prior to the singulation step. In other words,the substrate 102 may be singulated with or without the protective layer202. For example, the substrate 102 may be coated with a protectivelayer (such as the layer 202, for example) before the singulation stepto prevent dicing debris from mechanical dicing (e.g., sawing) fromadhering to the wiring layer 108 during singulation, and to allow thedicing debris to be removed along with the protective layer 202.

In various embodiments, other protective layer combinations (and anynumber of protective layers) may be used to protect underlying layersfrom the effects of process steps. Each protective layer may bechemically engineered to be selectively removed, while a layer below theprotective layer being removed protects underlying layers, such as thewiring layer 108, for instance. An organic layer may be hydrophobic orhydrophilic to act as an affinity for a solvent used. For example, atwo-layer combination may include two photoresist layers, onehydrophobic layer and one inorganic layer, or the like. A combination ofthree or more protective layers may also be used in a similar way, aseach layer acts to protect a lower layer from negative effects ofprocessing. In general, ensuring that the wiring layer 108 is notdegraded by metal removal or roughing of the topography is the goal ofthe one or more protective layers. In various embodiments, after the wetcleaning steps, the processed substrates or dies may be furtherprocessed prior to bonding to another clean dielectric surface.

CONCLUSION

Although the implementations of the disclosure have been described inlanguage specific to structural features and/or methodological acts, itis to be understood that the implementations are not necessarily limitedto the specific features or acts described. Rather, the specificfeatures and acts are disclosed as representative forms of implementingexample devices and techniques.

Each claim of this document constitutes a separate embodiment, andembodiments that combine different claims and/or different embodimentsare within the scope of the disclosure and will be apparent to those ofordinary skill in the art upon reviewing this disclosure.

1. A method of forming a microelectronic assembly, comprising: providing a first substrate having an exposed conductive wiring layer level with or below a bonding surface of the first substrate; coating the conductive wiring layer with one or more protective sacrificial layers; bonding a second substrate to the one or more protective sacrificial layers using a temporary bonding layer; removing the second substrate; removing the temporary bonding layer; exposing the first substrate, the one or more protective sacrificial layers, and a residue of the temporary bonding layer to a wet etchant for a preselected duration of time, the wet etchant decomposing at least one protective sacrificial layer, wherein the wet etchant comprises a complexing agent adapted to suppress dissolution of the conductive wiring layer; and washing said at least one protective sacrificial layer and the residue of the temporary bonding layer from the conductive wiring layer. 2-20. (canceled) 